Natural Resources Conservation Service
6200 JeffersonNE
Albuquerque, New Mexico 87109
Phone: (505) 761-4400 Fax: (505) 761-4462
Web site:
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October 5, 2004
New Mexico AGRONOMY TECHNICAL NOTE NO.42 revised
SUBJECT:ECS Soil Conditioning Index for Cropland Management Systems
Purpose:To distribute a revision to Agronomy Technical Note No. 42.
Effective Date:When contents have been noted.
Filing Instructions:Discard when noted.
Instructions:The Soil Conditioning Index (SCI) procedure is now part of the Revised Universal Soil Loss Equation,version 2 (RUSLE 2) and is to be used in conjunction with planning the conservation practice “Conservation Crop Rotation” (328). Save a copy of the RUSLE 2 run showing the SCI value and enter the correct value on the “Conservation Crop Rotation” (328) Jobsheet. File completed worksheets in the producer’s case file.
We will no longer use the SCI spreadsheet version of the index. Please remove any FO versions of the spread sheet and use the RUSLE 2 software to run the index. Forward comments about the procedure to State Conservation Agronomist
KENNETH B. LEITING
State Resource Conservationist
Attachment
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AC (4)
DC (37)
Ecological Sciences Division, Washington, DC (2)
Adjoining States — UT, CO, TX, OK, AZ (1 each)
Technical Services (1 file)
TECHNICAL NOTES
U.S. DEPARTMENT OF AGRICULTURENATURAL RESOURCES CONSERVATION SERVICE
NEW MEXICORevised September, 2004
AGRONOMY TECHNICAL NOTE NO. 42
SOIL CONDITION INDEX FOR NEW MEXICO
History
Up through the end of FY 2004, NM NRCS used a stand alone Excel spreadsheet to evaluate soil condition. The Revised Universal Soil Loss Equation version 2 (RUSLE 2) was revised and implemented in New Mexico near the end of FY 2004. The Soil Condition Index (SCI) was added to the RUSLE 2 equation and the old spreadsheet was discontinued.
Currently
The Excel spreadsheet version of the Soil Conditioning Index is now obsolete and will not be maintained. The SCI has been incorporated into RUSLE2 (the Revised Universal Soil Loss Equation). RUSLE 2 program can be downloaded from: The NM RUSLE 2 database can be downloaded from All new planning must now use the RUSLE 2 version of SCI.
RUSLE2 now gives three results: an improved soil loss estimate (water erosion), a soil organic matter trend estimate from the SCI, and a Soil Tillage Intensity Rating(STIR)number for use in making residue management decisions. The SCI works better within RUSLE2 than as a stand-alone spreadsheet because the climate data is more detailed, irrigation conditions are handled more realistically, and the erosion prediction is improved. Because of the modifications to the model, results from the SCI spreadsheet should not be compared to results from the RUSLE2 version of SCI.
The RUSLE2 version of the SCI was shown to be accurate in predicting soil organic matter trends by testing it with soil organic carbon data from long-term experiments across the country. This is the same set of data used to validate the spreadsheet version as described in national Soil Quality - Agronomy Technical Note 16: Interpreting the Soil Conditioning Index: A Tool for Measuring Soil Organic Matter Trends (280KB) <
Description
The Soil Conditioning Index (SCI) is a tool that can predict the consequences of cropping systems and tillage practices on the trend of soil organic matter. Organic matter is a primary indicator of soil quality and an important factor in carbon sequestration and global climate change.
The Soil Conditioning Index has three main components: 1) the amount of organic material returned to or removed from the soil; 2) the effects of tillage and field operations on organic matter decomposition; and 3) the effect of predicted soil erosion associated with the management system. The SCI gives an overall rating based on these components. If the rating is a negative value, the system is predicted to have declining soil organic matter. If the rating is a positive value, the system is predicted to have increasing soil organic matter.
SCI is meant to be an easy-to-use field tool to generate qualitative and semi-quantitative estimates of trends in the soil resource.
The model is designed to aid Natural Resources Conservation Service (NRCS) and Conservation District staffs in planning and designing cropping systems and residue management practices to resolve low organic matter, poor soil tilth, and other soil quality-related problems during conservation planning.
The model was developed by personnel at the NRCSNationalSoilSurveyCenter in Lincoln, Nebraska.
Why is the SCI important?
The SCI is a quick way to characterize the organic matter dynamics of a farming system. Organic matter is a critical component of soil function for several reasons. Surface residue protects soil from the impact of rain and wind. As residue decays, it feeds microbes that improve soil structure and infiltration, and thus reduces runoff. Soil organic matter contributes to nutrient and water holding capacities. Regular inputs of organic material foster a diverse microbial community that supports plant health and productivity.
The SCI along with RUSLE2 can help assess two basic components of good soil management: building organic matter and controlling erosion.
When to use the SCI?
The SCI is a component of several practice standards in NRCS technical guides. It is designed to help you plan and design Conservation Crop Rotations and Residue Management practices when low organic matter, poor soil tilth, surface crusting, or erosion are identified as concerns. You can run several “what if” scenarios with the client so farmers can see for themselves which changes will have more or less effect on improving the status of soil organic matter. Several Practice Standards (e.g., Conservation Crop Rotation (328) Crop Residue Management (344) using the SCI to identify a cropping system that will achieve a specified purpose.
The SCI is not a soil quality index. It assesses only one component of soil quality (i.e., soil organic matter or SOM). It does not tell you what level of SOM you "ought" to have, but it will predict if a particular management system will have a positive or negative trend in SOM. Use the SCI to help you discuss and assess the effect of management choices on organic matter dynamics, but do not expect it to replace direct measures of SOM, or evaluations of other aspects of soil quality such as salinity, surface structure, runoff, or compaction.
What do the numbers mean?
If the calculated index is a negative value, soil organic matter levels are predicted to decline under that production system. If the index is a positive value, soil organic matter levels are predicted to increase under that system.
If the SCI value is negative, note which sub-factor(s) are influencing it the most. Modify the scenario by changing crops or field operations to develop alternatives for consideration by the producer.
The results cannot be used to predict the amount of organic matter or the rate of change. For example, if you are comparing two scenarios and one generates an SCI value of 0.4 and the second generates an SCI of 0.2, you cannot say the first will store twice as much SOM or store it twice as fast as the second. You can say that carbon and organic matter levels under both systems will increase, and you can be more certain of seeing a significant increase under the first scenario.
The SCI does not indicate a desirable or target level of soil organic matter. For example, a near-zero SCI value indicates that soil organic matter levels are probably being maintained, but soil health may still be poor if the soil organic matter is being maintained at a low level.
If a farmer switches to a system that will improve soil organic matter levels, help the producer plan how to monitor the changes or explain what changes to expect. It may take several years to measure an increase in SOM, but soil aggregation, infiltration and the soil biological community are likely to improve more quickly.
Cautions
Do not use the SCI as a sole assessment of soil quality or conservation planning. The SCI may produce misleading results when one of the components is near zero. For example, if you have very low erosion because of flat slopes or if you have extremely high yields that balance out the tillage losses of OM, you may get a positive SCI even though organic matter quality is poor and soil quality is poor. As with any model or assessment, the SCI should be used in combination with other observations and evaluations. If you see problems with infiltration, runoff, aggregation, or other soil quality concerns, the field evaluation should take precedence over the model, and conservation practices should be planned to address the soil quality problem.
Organic matter is an important factor determining soil quality in many systems, but it is not the only factor. Other important aspects of soil quality include quality of organic matter, salinity, sodicity, sedimentation, soil biota, nutrient management, contaminants, and effects of irrigation management. These are not reflected in the Soil Conditioning Index.